Cermet resistor elements and their method of manufacture are well known. These resistor elements consist of an electrically non-conducting base with a glass material containing conducting or semi-conducting materials, coated thereon. Such elements can be used for various electrical resistors including variable resistors and potentiometers. Electrical leads are connected to each end of the cermet resistor element in electrical contact therewith. In variable resistor and potentiometer applications, a wiper contact is moved in contact with the surface of the resistor. The degree of conductivity between the contact and the surface of the cermet determines the contact resistance variation (CRV) and the electrical noise of the variable resistor or potentiometer. To improve the CRV and to decrease the electrical noise, small quantities of highly conducting metal such as gold have been used in the composition of the resistance material. The gold ultimately deposits in minute particles on the top surface of the cermet, improving the conductivity between the contact and the cermet material. Silver, which is also highly conductive, has not been generally used for this purpose due to the tendency of silver ions to migrate in the presence of a direct current field.
The use of gold to improve the CRV in cermet resistors is very costly due to the continuing increase in cost of gold, and although silver has also increased in price, it is considerably less expensive than gold. The present invention contemplates the use of a silver-gold alloy which reduces the cost of the materials used while maintaining the low CRV and low electrical noise characteristics of gold and reduces the migration characteristics of the silver. Based on test results with and without the silver-gold alloy in the resistance material, the alloy apparently does not significantly affect the bulk resistivity of the resistance element. Spectroscopic analysis and electron microscope studies indicate that the gold-silver alloy particles reside on the surface of the cermet material while a small number of particles of the alloy are dispersed throughout the cermet material. The particles dispersed in the material are, apparently, not of a size and quantity to alter the resistivity beyond the normal variations encountered with this type of material.